The present invention relates to control systems for compensating for machine tool wear which respond to the measurement of a part which has been machined by a boring machine or the like and which adjusts the cutter or tool of the boring machine so that a subsequently machined part is expected to have a desired dimension.
The present invention provides an improved controlled system for compensating for machine tool wear which advantageously adjusts the cutter or tool of the machine the entire amount which appears necessary to bring a subsequently machined part to a desired dimension in a single tool adjusting step and which advantageously is capable of adjusting the cutter in either of two directions for compensating for temperature variations and the like. Preferably, the control system of the present invention is used in combination with a gaging unit which measures a machined part and provides an analogue error signal representative of the magnitude and the direction of the deviation of the machined part dimension from a standard or nominal dimension.
The preferred exemplary control system of this invention includes a memory for memorizing the analogue error signal from the gaging unit, an upper limit comparator to determine when a predetermined upper limit relative to the nominal dimension is exceeded, and a lower limit comparator to determine when a predetermined lower limit relative to the nominal dimension is exceeded. If neither the upper limit nor the lower limit is exceeded, the tool is adjusted an amount equal to the deviation and in opposite direction to expectantly bring a subsequently machined part to the nominal dimension. If either the upper or the lower limit is exceeded, the number of parts in succession which exceed that upper or lower limit are counted, but the tool is not immediately adjusted. Once a predetermined number of successive machined parts have been found to exceed one of the upper or lower limits, three for example, the tool is adjusted an amount to expectantly bring a subsequently machined part to the nominal dimension. The tool is not adjusted after a single determination that a machined part exceeds the upper or lower limit since changes in dimension due to tool wear are likely to be small since tool wear is normally gradual, and consequently, if a large change in dimension of a machined part is experienced, it is presumed that the change is probably due to an isolated change in material hardness. Once a predetermined number of parts, in this case three, have been found to exceed an upper or lower limit, it is presumed that rapid tool wear has occurred, and therefore, an appropriate adjustment to the tool is required.
The cutter or tool adjusting mechanism which is used in combination with the control system of this invention preferably has an accesible cylindrical surface on a member which is rotatable for adjustment of the tool toward and away from the tool support member, i.e. the boring bar of a boring machine. This cylindrical surface, in response to the output of the control system, may be gripped by a collet chuck or the like which is rotatably driven by a servo motor. A feedback signal is provided by a tachometer which is coupled to the servo motor for indicating the actual amount that the tool was adjusted. The tool adjusting mechanism is capable of adjusting the position of the tool to a variable degree so that the tool may be adjusted in one adjustment operation to the exact position required to expectantly bring a subsequently machined part to the nominal dimensions. Moreover, the combination of a collet chuck and a tool adjusting member having a grippable cylindrical surface simplifies tool set up and alignment of the adjusting mechanism portion driven by the servo motor with the adjusting mechanism portion on the tool support member since the cylindrical surface can be engaged at any rotational alignment of the collet chuck.
Other advantages and features of the present invention will be apparent in view of the Detailed Description of the Preferred Embodiment presented hereinafter.